Options may be set by specifying -optionvalue in the
FFmpeg tools, option=value for the aresample filter,
by setting the value explicitly in the
SwrContext options or using the libavutil/opt.h API for
programmatic use.

ich, in_channel_count

Set the number of input channels. Default value is 0. Setting this
value is not mandatory if the corresponding channel layout
in_channel_layout is set.

och, out_channel_count

Set the number of output channels. Default value is 0. Setting this
value is not mandatory if the corresponding channel layout
out_channel_layout is set.

uch, used_channel_count

Set the number of used input channels. Default value is 0. This option is
only used for special remapping.

isr, in_sample_rate

Set the input sample rate. Default value is 0.

osr, out_sample_rate

Set the output sample rate. Default value is 0.

isf, in_sample_fmt

Specify the input sample format. It is set by default to none.

osf, out_sample_fmt

Specify the output sample format. It is set by default to none.

tsf, internal_sample_fmt

Set the internal sample format. Default value is none.
This will automatically be chosen when it is not explicitly set.

For swr only, set resampling phase shift, default value is 10, and must be in
the interval [0,30].

linear_interp

Use linear interpolation when enabled (the default). Disable it if you want
to preserve speed instead of quality when exact_rational fails.

exact_rational

For swr only, when enabled, try to use exact phase_count based on input and
output sample rate. However, if it is larger than 1 << phase_shift,
the phase_count will be 1 << phase_shift as fallback. Default is enabled.

cutoff

Set cutoff frequency (swr: 6dB point; soxr: 0dB point) ratio; must be a float
value between 0 and 1. Default value is 0.97 with swr, and 0.91 with soxr
(which, with a sample-rate of 44100, preserves the entire audio band to 20kHz).

precision

For soxr only, the precision in bits to which the resampled signal will be
calculated. The default value of 20 (which, with suitable dithering, is
appropriate for a destination bit-depth of 16) gives SoX’s ’High Quality’; a
value of 28 gives SoX’s ’Very High Quality’.

For swr only, simple 1 parameter audio sync to timestamps using stretching,
squeezing, filling and trimming. Setting this to 1 will enable filling and
trimming, larger values represent the maximum amount in samples that the data
may be stretched or squeezed for each second.
Default value is 0, thus no compensation is applied to make the samples match
the audio timestamps.

first_pts

For swr only, assume the first pts should be this value. The time unit is 1 / sample rate.
This allows for padding/trimming at the start of stream. By default, no
assumption is made about the first frame’s expected pts, so no padding or
trimming is done. For example, this could be set to 0 to pad the beginning with
silence if an audio stream starts after the video stream or to trim any samples
with a negative pts due to encoder delay.

min_comp

For swr only, set the minimum difference between timestamps and audio data (in
seconds) to trigger stretching/squeezing/filling or trimming of the
data to make it match the timestamps. The default is that
stretching/squeezing/filling and trimming is disabled
(min_comp = FLT_MAX).

min_hard_comp

For swr only, set the minimum difference between timestamps and audio data (in
seconds) to trigger adding/dropping samples to make it match the
timestamps. This option effectively is a threshold to select between
hard (trim/fill) and soft (squeeze/stretch) compensation. Note that
all compensation is by default disabled through min_comp.
The default is 0.1.

comp_duration

For swr only, set duration (in seconds) over which data is stretched/squeezed
to make it match the timestamps. Must be a non-negative double float value,
default value is 1.0.

max_soft_comp

For swr only, set maximum factor by which data is stretched/squeezed to make it
match the timestamps. Must be a non-negative double float value, default value
is 0.

For details about the authorship, see the Git history of the project
(git://source.ffmpeg.org/ffmpeg), e.g. by typing the command
git log in the FFmpeg source directory, or browsing the
online repository at http://source.ffmpeg.org.

Maintainers for the specific components are listed in the file
MAINTAINERS in the source code tree.